1. Field of the Invention
This invention relates to obtaining high purity crystalline fructose in high yields.
2. Description of the Art Practices
Fructose is commonly used as a high fructose syrup in the soft drink and cookie mix industries because of its high sweetening power in relation to its weight. Fructose is more than twice as sweet as table sugar (sucrose) when used on an equivalent weight basis.
The fructose is typically produced by hydrolyzing corn starch to dextrose (glucose), isomerizing the dextrose substantially to fructose, and selling the resultant mixture of dextrose and fructose as a liquid syrup. Of course, the liquid syrup is not aesthetically desirable as a sucrose substitute for consumer uses. While fructose has many institutional uses as a syrup, it has not been successfully commercialized as a dry powder to consumers. As fructose is considerably sweeter than sucrose, it is desirable to obtain crystalline fructose which would aid diet-conscious persons by giving an equivalent level of sweetening at a substantially reduced caloric intake level.
As fructose is obtained as a syrup in mixtures with dextrose which is not as sweet as fructose, it is desirable that the dextrose be removed. The difference while not noticeable on a taste basis, nonetheless adds extra calories without the desired sweetening benefit.
Another factor which must be considered in the processing of fructose to give a substantially crystalline powder is the high solubility of fructose in water. As previously noted, the conversion of starch to dextrose and the dextrose to fructose syrup is accomplished in the presence of water. While the high solubility of fructose presents substantial difficulties in obtaining crystalline fructose, it is nonetheless beneficial in that an aqueous dispersion containing fructose is relatively easy to transport and pump with a substantial solids content.
U.S. Pat. No. 3,607,392 issued Sept. 21, 1971 to Lauer describes a process and apparatus for obtaining crystalline fructose through the use of methanol. Methanol has limits on its usage in food products which is the major market for crystalline fructose in the first instance. Forsberg et al in U.S. Pat. No. 3,883,365 issued May 13, 1975 describes the separation of fructose from dextrose within a narrowly constrained pH range by lowering the temperature of the reaction mixture. The disadvantage in the Forsberg et al process is that it is not economical to refrigerate a syrup. Typically, the syrups containing fructose are at a minimum of 30.degree. C. due to the high temperature processing conditions and simply to maintain the syrup in a fluid state. The refrigeration of a syrup therefore requires a substantial degree of energy and equipment to remove the heat in the syrup.
Yamauchi U.S. Pat. No. 3,928,062 issued Dec. 23, 1975 describes recovering fructose by seeding anhydrous fructose crystals into a supersaturated solution of fructose. Kubota in U.S. Pat. No. 4,371,402 issued Feb. 1, 1983 states that the dehydration of fructose occurs utilizing an organic solvent having azeotropic behavior with respect to water.
Dwivedi et al in U.S. Pat. No. 4,199,373 issued Apr. 22, 1980 describes obtaining anhydrous free-flowing crystalline fructose by allowing a seeded syrup to stand at a low temperature and high relative humidity. U.S. Pat. No. 4,199,374 also issued on Apr. 22, 1980 to Dwivedi et al suggests seeding a syrup containing fructose and allowing it to stand followed by recovery of the fructose. U.S. Pat. No. 3,513,023 to Kusch et al issued May 19, 1970 discloses the recovery of crystalline fructose over a broad pH range through concentration and cooling, followed by seeding of the mixture.
Two substantial difficulties have been recognized in the art in the production of crystalline fructose. The first problem is to remove water from the syrup thereby placing the fructose in a condition where it may crystallize. As previously noted, the high solubility of the fructose requires that the water be substantially removed as it is not otherwise possible to obtain the crystalline fructose. The method such as that described in Kubota is too difficult to practice inasmuch as the addition of alcohol to the syrup can result in a gummy mass. The gummy nature of the syrup following alcohol addition under ordinary procedures is such that fructose cannot be crystallized. When crystallization does occur in the gummy mass, it is likely as not to foul the pumps or transfer lines within the reactors. Of course, any dextrose or other material in the syrup at that time will necessarily be trapped within the gummy mass and therefore the purity of the fructose will be substantially lessened.
The second problem in obtaining crystalline fructose is to obtain the material in a particle size distribution similar to sucrose. The particle size distribution is a function of avoiding the gummy mass as this phenomena overwhelms the controlled seeding required in obtaining the desired crystals.
It is therefore desirable that a method be devised for the production of crystalline fructose through the use of alcohols to disassociate the water in the syrup from the fructose wherein the syrup is stable and supersaturated with regard to the fructose.
Throughout the specification and claims, percentages and ratios are by weight, temperatures are in degrees Celsius, and pressures are at atmospheres over ambient unless otherwise indicated. To the extent that any of the references mentioned herein are applicable to the present invention, they are incorporated by reference.